Both agonists and antagonists of the strychnine-insensitive glycine site of N-methyl-D-aspartate receptors modulate polysynaptic excitations in slices of mouse olfactory cortex.
In this study, it is reported that bath application of D-serine and, to a lesser extent glycine, potentiated polysynaptic but not monosynaptic excitations evoked in slices of mouse olfactory cortex perfused with solution containing Mg2+ (1 mmol/l), picrotoxin and strychnine (both 25 mumol/l). Effects were largely confined to the longer latency components of the field potentials and occurred at amino acid concentrations of between 0.01 and 1 mmol/l. The effects of D-serine and glycine were antagonized by 7-chlorokynurenate and indole-2-carboxylate, antagonists of the glycine regulatory site of the N-methyl-Daspartate (NMDA) receptor complex. D-Serine (glycine not tested) also potentiated, and 7-chlorokynurenate partially inhibited the longer latency components of the polysynaptic field potentials evoked in slices perfused in the absence of picrotoxin and strychnine. However, neither D-serine nor glycine potentiated responses evoked by the bath application of NMDA. It is concluded that under the present experimental conditions, the glycine regulatory sites of those NMDA receptor involved in the mediation of polysynaptic excitations in the mouse olfactory cortex are not saturated with endogenous glycine.